The present invention relates to a device for positioning and firmly holding a test strip for optical-medical measurements, this device comprising a housing with a reception opening having a stop for the test strip on the inner end thereof and with a window which is positioned opposite the test zone of a test strip when the test strip is inserted into the reception opening and lies against the stop.
The precise positioning of a medical test strip in an appropriate evaluation device, usually a remission photometer, is of decisive importance for the exactitude of the evaluation of the test strip. On the one hand, it is, of course, important that the test strip lies, in the longitudinal direction, correctly below the window of the optical measuring device in order that only the appropriate test zone lies in the measurement area and not perhaps a part of the carrier material which would falsify the measurement result. On the other hand, it is extremely important that the distance between the optical measuring device and the surface of the test zone can be reproduced very precisely because, depending upon the construction of the optical system, the measured intensity enters into the result with the second to fourth power of the distance between the measurement field and the photoreceiver. In the case of a typical distance of 8 mm., a variation of the distance of only 0.1 mm. gives an error which is from 2.5 to 5%. Special difficulties arise from the fact that, if possible, test strips of different manufacture and for different medical parameters are to be measured with one apparatus. The thickness of these test strips can differ considerably in the region of the test zone.
In the case of a known apparatus, the test strips are introduced into a device provided therefor and firmly held in the measurement position by means of a leaf spring. In these devices, positioning is unsatisfactory not only in the longitudinal direction of the test strip but also with regard to the distance from the optical measurement system. It can happen relatively easily that when the test strip is inserted, it does not lie completely against the stop because the leaf spring has already exerted a considerable resistance to the insertion. On the other hand, it can also quite easily happen that the test strip, after insertion, is inadvertently pulled out of the apparatus to a small extent due to the fact that especially when the hands of the person operating the device are moist, which can frequently occur in a laboratory, the fingers stick somewhat to the test strip.
Furthermore, as has been recognized by applicants, positioning at right-angles to the surface of the test strip can also be insufficiently exact when test strips of varying thickness are to be measured. Thus, the tension of the leaf spring is, to a considerable extent, dependent upon the thickness of the test strip. The distance between the test zone and the optical measurement system also changes correspondingly to an extent which is unacceptable when a high degree of exactitude of the measurement is required.
Oftentimes the window in the reception opening has to be an open frame (e.g. to allow air to be in contact with the test piece) and in these cases the unsatisfactory results with known devices can easily be explained by the fact that different test zones are pressed into this frame to a different extent. However, as the present inventors found, also in apparatus with a firmly positioned closed window (e.g. by glass) the measuring results depend in most cases heavily on the strength of the force by which the test zone is pressed against the window.